The present invention relates to a wafer transforming device and, more particularly, to a device for transforming a base material according to the shape of a mask when a pattern, formed on the mask is to be transferred onto a resist film formed on the surface of the base material.
An IC (integrated circuit) or LSI (large-scale integrated circuit), for example, is manufactured with a required circuit arrangement by forming a resist film on a wafer made of silicon, transferring to the resist film a required pattern formed on a mask, and repeatedly performing the processing of etching, ion implantation, etc. according to the transferred pattern.
In, for example, the IC and the LSI, for enhancing a density of integration more, it is required to form a fine pattern in which the width of a line forming the circuit is 1 .mu.m or less and, to met such requirement, it has been proposed to employ soft X-rays for the transfer of the pattern.
Several X-ray exposure apparatuses employing the soft X-rays; however, it is known that soft X-rays decay considerably in proceeding from a generation source to the resist film formed on the wafer. Therefore, various proposals have been made which include, for example, the measure of increasing the generation dose of the soft X-rays and the X-ray source, the measure of forming the mask by the use of a material which easily transmits the soft X-rays and also a maximum thinning of the mask.
When the mask is thinned, the mechanical strength of the mask lowers to such an extent that a large mask cannot be fabricated. Therefore, a step-and-repeat type transfer method has been proposed in which a mask corresponding to one LSI is prepared, and the wafers are moved one by one after the corresponding pattern has been transferred. However, when the mask is thin, it is difficult to flatten the mask.
On the other hand, the soft X-rays propagate rectilinearly while spreading radially from the generation source. In addition, the generation source of the soft X-rays has a size which corresponds to a diameter of an electron beam to irradiate an anode. Consequently, a deviation, corresponding to the size of the generation source, affects the arrival position of the soft X-rays which propagate from the generation source through the mask to the resist film on the wafer. This gives rise to defocusing, or a shift to a position somewhat deviating from a position directly under the mask pattern.
Moreover, the mask undergoes various unfavorable influences which include, for example, errors in fabrication of the mask, a distortion attributable to temperature rise at the exposure, a deformation attributable to chucking in the case of setting the mask on the exposure apparatus, a distortion attributable to the weight of the mask itself, and a distortion attributable to the difference between pressures acting on the upper and lower surfaces of the mask. When the mask is repeatedly used, it also undergoes a distortion ascribable to a change-with-time thereof. On the other hand, the wafer undergoes various unfavorable influences which include a deformation in the fabrication of the mask, a deformation attributable to chucking in the case of setting the wafer on the exposure apparatus, and deformations incurred in such processes as etching and ion implantation.
Accordingly, in order to transfer the circuit pattern of 1 .mu.m or less, the surface part of the wafer to be exposed to the soft X-rays is required to be transformed so that the pattern projected from the mask can be received in the best condition.
In order to meet such requirement, an exposure device is proposed in, for example, IBM Technical Disclosure Bulletin, Vol. 15, No. 10, March 1973, entitled "Flatness Controlled Wafer Clamping Pedestal", wherein piezoelectric elements are arranged on the clamping pedestal formed with an opening for vacuum suction, with a wafer being placed on the pedestal and held in the vacuum suction, and, with a height of a plurality of points on the front surface of the wafer being detected by sensors. On the basis of the detected results, required voltages are applied to the piezoelectric elements, so as to push up the rear surface of the wafer so that the front surface of the water is made horizontal.
A disadvantage of this proposed device resides in the fact that, when the wafer is pushed up by the piezoelectric elements, a gap appears between the pedestal and the wafer resulting in a weakening of the vacuum force holding the wafer and the wafer is liable to slip due to air current flowing through the gap. Further, unless the piezoelectric elements are arranged uniformly over the whole area of the wafer, the wafer cannot be transformed to be horizontal or into a required shape. Therefore, for example, one hundred five piezoelectric elements are required, with the piezoelectric elements being arranged at intervals of 10 mm along the entire surface of a four-inch wafer, and one hundred forty-nine piezoelectric elements are required in a case of a five-inch wafer. Consequently, it is necessary to provide the same drive means for the piezoelectric elements and, since the drive means usually need to apply voltages of 0-650 V to the piezoelectric elements, it is technically difficult to provide a small side device. Since, it is technically difficult to furnish the exposure device with a large number of drive means, the device becomes unnecessarily large in size as well as relatively expensive.
An object of the present invention is to provide a wafer transforming device wherein there is no reduction in the force holding for the wafer, and therein the number of drive means for piezoelectric elements is equal to that of the piezoelectric elements to be actuated at one exposure, thereby permitting an exposure apparatus to be small in size and have an enhanced exposure precision.
In order to accomplish the object, according to the present invention, a diaphragm type chuck is arranged on the wafer placing surface of a chuck case, with the lower surface of the chuck being supported by a large number of vertically moving elements and held in vacuum suction so as to be in close contact with the upper ends of the vertically moving elements, and with the vertically moving elements lying in an exposure region and surrounding area thereof being switched and connected to a drive means.